Construction of the lower part of the crucible of igneous electrolysis cells



Aug. 5, 1958 p. MOREL 2,846,388

CONSTRUCTION OF THE LOWER PART OF THE CRUCIBLE v 0F' IGNEOUSELECTROLYSIS CELLS x Filed April 23, 1956 2 Sheets-Sheet 1 Fiel 'f 3 INVENTOR Paul Morel Fic-1.4

Aug. 5, 1958 OF IGNEOUS ELECTROLYSIS CELLS Filed April 23, 1956 P. MOREL2, CONSTRUCTION OF THE LOWER PART OF THE ORUOTBLE 'Paul 2 Sheets-Sheet 2IN VE NTOR Morel BY Mza/7 A ATTORNEY United States Patent CONSTRUCTIONOF THE LOWER PART OF THE CRUCIBLE OF IGNEOUS ELECTROLYSISv CELLS PaulMorel, Hermillon,v France, assigrnor to `Perchiney Compagnie de ProduitsChimiques et Electrometallurgiques, Paris, France, acorporation ofFrance Cells for use inigneous'electrolysis and, more particularly,those intended 'for the manufacture of alumi-V num, operate at lowvoltages, at times ofthe order of 4 to 4.5 volts, p Accordingly, it isimportant to reduce as far as possible the various voltage drops whichare useless in the electrolysis. In French Patent No. 953,361, there arealready described methods for insuring the electrical connection betweenthe carbon Iblocks forming the bottom ofthe crucible of the electrolysiscell and the metallic bars for the current inlet or outlet (dependingwhether the operation relates to the production of aluminum byrelectrolysis, or the refining of this metal). yIn accordance with thosemethods, the steel bars-generally of rectangular cross-section-aresealed in grooves provided in the carbon blocks by means of cast-iron ofwell the surface of the cruciblebottom to a size which'isV approximatelyequal to the surface of the anode assembly. In this manner, it ispossible to decrease thev magnitude of level variation and movement ofliquid aluminum in the bottom of the cell crucible, and it is possibleto obtain thereby very high electrolysis yields which attain, andsometimes even exceed, 90%.

On the other hand, inasmuch as the active surface of the crucible bottomhas been reduced by the presence of these sloping banks, the voltagedrop increases and frequently attains 0.40 volt. It is accordingly quiteimportant to` reduce this voltage drop without modifying the new methodsof operating electrolysis cells.

The present invention, which is based on applicants investigations,solves this problem. It is based on the fact that the largest part ofthe voltage drop in the crucible bottom is due to the electricresistance of the steel bars which insure the` connection between thecarbon blocks and the external conductors. Hence, the inventioncomprises means for increasing the electric conductivity of thisconnection, which may be realized by several embodiments of theinvention.

According to a first embodiment of the invention, the cross-sectionprovided for the passage of the current is increased by adopting thickersteel bars, or by welding to at least one surface of the steel bar acopper bar. This embodiment is carried out without changing the totallength of the bars.

The copper bar can be welded onto that face of the steel bar which isnot in contact with the cast-iron seal. It can equally be welded to alateral face of the steel bar, the copper bar being then partiallyimmersed in the liquid cast-iron at the time when the steel bar issealed in the grooves provided in the carbon blocks. The currentproceeding from the blocks can then pass directly into the copper.

Mice

According to a secondembodiment of the invention, I

the length of the steel bars is reduced, this being made possible by acorresponding reduction in the width of the lower part of the cell. Thelength of steel thus elimi- .nated can be replaced by aluminumconductors the ele`c tric conductivity of which is better. Steel barshaving a large cross-section can be used o1' else, they can bereinforced by a copper bar.

According to a third embodiment of theinvention,'the width yof the lowerportion of the cell is not modied, but the connecting bars extendthrough Athe bottom of the cell, either by bending them at right anglesimmediately opposite the external edge of the carbon blocks, or bygiving them a convenient shape.

The annexed diagrammatic figures will give a better understanding of theinvention. Of these,

Figure 1 represents a transverse Vertical section of an electrolysiscell constructed according to the prior art; it is the purpose of thepresent invention to improve such construction;

Figures 2 and 3 represent transverse vertical sections p of two variantsof the iirst embodiment of the invention;

' Figure 4 represents to an enlarged scale a partial crosssection,through a vertical plane perpendicular to that of Figure 3, of a detail;

Figures 5 and 6 represent transverse vertical sections of two variantsof the second embodiment of the invention;

Figures 7 and 8 represent transverse vertical sections of two variantsof the third embodiment of the invention.

The same reference numerals designate the sameor corresponding parts inthe several figures.

1 designates the metallic casing which surrounds the cell, 2 aninsulating layer, 3 the carbon walls of the crucible, 4 the carbonblocks forming the bottom of the cell and comprising at their lower parta groove in ywhich the steel bar 5 is sealed in by cast-iron. 6designates a foundation formed of refractory insulating bricks on whichthe crucible rests. y l

As will be seen from Figure l, the steel bar 5 does not extend at thebottom beyond the lower part of the carbon blocks and, as a result, itsdimensions are limited.

When the cell is operated at relatively low temperatures,A

such as 930-950 C., and with Ilateral sloping vbanks of solid cryolite,the potential drop in the bottom of the'.

electrolysisr cell illustrated volt. K

In Figure 2, the bars 5 have'a 4cross-section triple that of those shownin Figure 1 and, as a result, the potential drop in the bottom isreduced to 0.30 volt. However, in this arrangement the bars penetratedeeply into the foundation 6 which complicates the construction;moreover, it is necessary that the bars be deeply notched at the placeswhere they pass into the casing 1 in order to avoid excessive weakeningof the latters strength.

To avoid these drawbacks, the arrangement illustrated in Figure 3 can beadopted. According to this variant of the invention, the lbar 5 retainsits original dimension as in Figure 1, but there is welded to its lowerpart a copper strip 7, either on the entire length of the steel bar, orwith an interruption underneath the central block, as shown in Figure 3.A copper strip having a cross-seo tion of mm. x 20 mm. is the equivalent(in conductivity), at the operating temperature, of steel bars 200 mm. xv mm., that is, sections 12 times larger. The potential drop is the sameas in Figure 2, namely 0.30.

Figure 4 represents to an enlarged scale a detail of a carbon blockadjacent a seal. As will be observed, the copper bar 7, welded to alateral face of the steel bar 5,

`in Figui-e1 amounts tol0l4() is surrounded by the cast-iron seal 8. Thecopper bar can be perforated, for example, at 9, in order to insureimproved connection between the cast-iron and the copper. By this means,there can be obtained a gain of about 0.03 volt as compared with thearrangement illustrated in Figure 3. 4That is, the potential drop is now0.027.

-Since for -equal conductivity aluminum is a cheaper conductor thansteel, provision is made according to the second embodiment of theinvention for ashortening in the length of the'steel `bars (Figure 5)and for the replacement of the eliminated ends by aluminum bars 11. Itis then necessary to decrease the width of the lower portion of thecasing because aluminum cannot withstand the temperatures prevailing,therein and, hence, must be disposed externally thereof.

Figure 5 represents such an arrangement using steel bars of largecross-section extending outside the bottoml of the groove provided inthe carbon blocks.

its lower part, but having steel bars which do not extend outside thegroove in the carbon blocks, the said bars being reinforced by a weldedcopper plate 7.

By adopting the arrangement represented in Figures 5 and 6, there isobtained a voltage drop of 0.25 volt in the bottom of the cell.

In the third embodiment of the invention, contraction of the lowerportion of the casing is avoided while shortening, nevertheless, theSteel bars. This result is obtained by passing out the end of the barsthrough the bottom of the cell.

In the arrangement of Figure 7, the bars are bent at right anglesopposite the blocks and the aluminum conductors 11 are then longer thanin `Figures 5 and 6. Moreover, it is possible to dispose underneath thecells the conductors 12 which collect the current from the steel bars.

The bent bars 5 can be strengthened by means'of a copper strip 7. It ispossible to obtain thereby a potential drop somewhat lower than 0.25,for example, a drop of 0.24.

In Figure 8, the steel bar 5 has exactly the same length as the assemblyof the bottom blocks; the current leaves through vertical steel bars.The assembly has approximately the shape of the Greek letter pi Thisshape can :be obtained either by forging or by welding. The potentialdrop in the bottom can readily amount to 0.24 volt.

It is evident that by welding a thicker sheet of copper onto the steel,it is posible to reduce still further the potential drop in the bottomof the cell, indeed, in all three embodiments above described. However,a lower potential drop necessitates increased thermal insulation,

hence, increased installation costs. The most favorable cross-sectionsand lengths of the steel, copper and aluminum conductors depend on theprice of these raw materials and the cost of the energy in theparticular region. A person skilled in the art can determine these ineach particular case without departing from the scope of the presentinvention. Y t

I claim:

l. A cell for use in igneous electrolysis comprising, in combination: alower portion provided with carbon blocks; grooves in said blocks;current conducting ferrous bars positioned in said grooves in contactwith said blocks, said bars having a length significantly shorter thanthe width of the cell at its upper portion; sloping banks of solidifiedmatter disposed all around the inner circumference of the cell; wherebythe active surface of the cell ybottom is decreased and the voltage dropin the bottom of the cell is detrimentally increased; and conductorshaving an electrical conductivity higher than that of said barsextending. from they ends of said bars and `forming means ot'attachmentto a source of current, whereby the potential drop in the bottom of thecell is advantageously decreased.

2. A cell according to claim l wherein the conducting bars are formed ofsteel, and the conductors of higher conductivity are formed of aluminum.

3. A cell for use in igneous electrolysis comprising, in combination: alower portion of contracted width relative to the top portion of thecell; carbon blocks in said lower portion; grooves in said blocks;current conducting ferrous bars positioned in said grooves in contactwith said blocks, said bars having a length substantially coextensivewith said contracted width; sloping banks of solidilied matterdisposedall around the inner circumference of the cell; whereby theactive surface of the cell bottom is decreased and the voltage drop inthe bottom of the cell is detrimentally increased; and conductors havingan electrical conductivity higher than that of said bars extending fromthe ends of said bars and forming means of attachment to a source ofcurrent, whereby the potential drop in the bottom of the cell isadvantageously decreased.

4. A cell according to claim 3, wherein the conducting bars are formedof steel, and the conductors of higher conductivity are formed ofaluminum.

References Cited in the le of this patent UNITED STATES PATENTS

1. A CELL FOR USE IN IGNEOUS ELECTROLYSIS COMPRISING, IN COMBINATION, ALOWER PORTION PROVIDED WITH CARBON BLOCKS, GROOVES IN SAID BLOCKS;CURRENT CONDUCTING FERROUS BARS POSITIONED IN SAID GROOVES IN CONTACTWITH SAID BLOCKS, SAID BARS HAVING A LENGTH SIGNIFICANTLY SHORTER THANTHE WIDTH OF THE CELL AT ITS UPPER PORTION; SLOPING BANKS OF SODIDIFIEDMATTER DISPOSED ALL AROUND THE INNER CIRCUMFERENCE OF THE CELL; WHEREBYTHE ACTIVE SURFACE OF THE CELL BOTTOM IS DECREASED AND THE VOLTAGE DROPIN THE BOTTOM OF THE CELL IS DETRIMENTALLY INCREASED; AND CONDUCTORSHAVING AN ELECTRICAL CONDUCTIVITY HIGHER THAN THAT OF SAID BARSEXTENDING FROM THE ENDS OF SAID BARS AND FORMING MEANS OF ATTACHMENT TOA SOURCE OF CURRENT, HEREBY THE POTENTIAL DROP IN THE BOTTOM OF THE CELLIS ADVANTAGEOUSLY DECREASED.